In a helical scanning type magnetic tape recorder, a flying erasing method has been mostly used for erasing signals recorded on a magnetic tape. A magnetic erasing system of the flying erase type includes a magnetic erase head from which an erasing magnetic field is generated.
One of conventional magnetic erasing systems is described on pages 869 to 871 in the report "IEEE TRANSACTIONS ON MAGNETICS", volume MAG 20, No. 5. In this report, a magnetic erase head is driven with an erase current of more than 100 mA, in which the relative tape-to-head speed is 3.8 m/s and an erase frequency is 5 MHz. In the report, the polarity of a magnetic field generated from the magnetic erase head is inverted twice to increase the erasing effect within a time in which a magnetic tape is moved over a length of one-thirds of a gap provided in a magnetic core.
According to the conventional magnetic erase system, however a large residual magnetization recorded by the erase head may be left on the magnetic tape due to the large erasing current of 100 mA as described before, so that crosstalk occurs on a reproduced signal. For the purpose of reducing this crosstalk, an azimuth angle is assigned to a recording and reproducing (read and write) head. However, this is not sufficient to remove crosstalk completely.
Further, where a magnetic tape having a high coercive force is used, it is difficult to erase the recorded signals completely. To solve such problem, it can be proposed that an erasing magnetic filed is increased by increasing the level of an erase current. However, a large electric power is required to drive the magnetic erase head. Further, it can be proposed that an erasing magnetic field is increased by increasing the winding number of the head coil turns. However, an impedance of the magnetic erase head is increased, so that a large electric power is required to drive the head.